So we’re still talking about election forecasts

Nate Silver responded to the stupidest available critique of his election forecast, while brushing off the most detailed one. (If you think this makes him a “radical centrist” then I’ve got a Thomas Friedman swimsuit calendar to sell you.) Everybody reality-based agrees that in Presidential election, the economy matters, the candidates matter, and all sorts of other stuff matters.

One thing that everyone should know, but not everyone does, is that the fit of a model to past data is usually much better than its fit to future data. People who don’t realise this tend to make their prediction intervals (not confidence intervals, please) too narrow. The pro solution is to split data into training and test sets, but this isn’t feasible for presidential elections. You still want to do some kind of out-of-sample validation. But all the ways of doing this are terribly flawed!